Injection molded bobbin basket

ABSTRACT

A bobbin basket for use with a lock-stitch sewing machine. The bobbin basket defines a receptacle for a thread-carrying bobbin case. The bobbin basket has a wall extending around a central axis and a rib projecting radially from the wall for reception in a raceway of a rotary loop taker, to which the bobbin basket can be operably connected. The bobbin basket is molded from a TORLON®-based material commercially sold under the designation PXM01017.

FIELD OF THE INVENTION

[0001] This invention relates to a bobbin basket for a lock-stitch sewing machine and, more particularly, to a molded bobbin basket made from a polymer material.

BACKGROUND OF THE INVENTION

[0002] This invention supplements the inventions disclosed and claimed in applicant's U.S. Pat. No. 4,858,543, issued Aug. 22, 1989, and U.S. Pat. No. 5,188,046, issued on Feb. 23, 1993, both assigned to the assignee of the present invention. The bobbin basket covered by U.S. Pat. No. 4,848,543 is adapted for use with a horizontal rotary loop taker (or “hook”). The invention in U.S. Pat. No. 5,188,046, and the present invention, are both useful with bobbin baskets adapted for use with a horizontal hook, a vertical hook, or a zigzag hook.

[0003] Sewing machine bobbin baskets are often made of metal, typically steel. The inventions covered by Patent Nos. 4,858,543 and 5,188,06 went long way toward providing a bobbin basket that avoids the problems long associated with steel bobbin baskets.

[0004] There are many advantages that a plastic bobbin basket has over a conventional all-steel basket. Molding of the basic plastic piece is far more convenient and less expensive than the casting or forging—followed by various machining, polishing and hardening steps—that is involved in the production of an all-steel bobbin basket. Chattering of the bearing rib in its raceway—which produces chipping and burring, with resulting thread breakage—is avoided with a plastic bobbin basket. The low coefficient of friction between the bearing rib, and a raceway in which it moves, accounts for potentially a longer life for the plastic bobbin basket, and may avoid the problems of messy lubrication, galling, bluing of a rotary loop taker, and puckering of the goods being sewn that accompany the use of an all-steel basket.

[0005] There are several plastic materials of a high wear and self-lubricating type that may be considered as being more or less suitable for the manufacture of a bobbin basket. Of these, the most suitable are the poly(amide-imide) resins, in which the polymer chain comprises amide linkages alternating with imide linkages. Poly(amide-imide) resins have exceptional mechanical strength and dimensional stability, and a low coefficient of thermal expansion. Furthermore, they maintain these properties at very high temperatures.

[0006] It was generally believed by skilled workers in this art in the early 1990's that the high melt viscosity of poly (amide-imide) resins, combined with the extremely complicated structure of bobbin baskets, made it impossible to use these polymers in producing such baskets by injection molding. However, the applicant successfully engineered and successfully commercially marketed, and continues to successfully market, injection molded bobbin baskets using poly(amide-imide) resins, and particularly ones incorporating resins sold commercially under the trademark TORLON®, owned by Amoco Performance Products, Inc.

[0007] While bobbin baskets using poly(amide-imide) resins have performed very well in the industry, designers of sewing equipment are constantly seeking ways to improve bobbin baskets by maintaining the desirable operating characteristics of the resin materials, while at the same time increasing the useful life of these baskets, primarily by reducing wear during use. As bobbin baskets wear, their operating characteristics may be altered. At the point that replacement becomes necessary, equipment must be shut down to allow the removal of the spent basket and installation of a new basket. Aside from the expense associated with a new basket and the labor costs associated with basket replacement, system down time may account for further significant, economic loss. Heretofore, to the knowledge of the applicant, while the call for improved wear characteristics for plastic bobbin baskets has been made by the industry, no significant, viable improvements in the baskets, over those made from currently used poly (amide-imide) resin baskets, have evolved over the last decade that afford better wear properties which translates into longer basket life.

SUMMARY OF THE INVENTION

[0008] In one form, the invention is directed to a bobbin basket for use with lock-stitch sewing machine. The bobbin basket defines a receptacle for a thread-carrying bobbin case. The bobbin basket has a wall extending around a central axis and a rib projecting radially from the wall for reception in a raceway of a rotary loop taker, to which the bobbin basket can be operably connected. The bobbin basket is molded from a TORLON®-based material commercially sold under the designation PXM01017.

[0009] In one form, the bobbin basket has a center post extending along the central axis in the receptacle for supporting a thread-carrying bobbin case.

[0010] In one form, at least the rib is made from the TORLON®-based material.

[0011] In one form, at least the wall is made from the TORLON®-based material.

[0012] The rib and wall may both be made from the TORLON®-based material.

[0013] The invention is further directed to the combination of a bobbin basket and a rotary loop taker with a raceway. The bobbin basket has a receptacle for a thread-carrying bobbin case, a wall extending around a central axis, and a rib projecting radially from the wall. The rib resides in the raceway and is guided within the raceway as relative movement of the bobbin basket and rotary loop taker around the central axis takes place with the bobbin basket and rotary loop taker operably connected. The bobbin basket is molded from a TORLON®-based material commercially sold under the designation PXM01017.

[0014] The bobbin basket may have a center post, as described above.

[0015] A part, or all, of the bobbin basket may be made from the TORLON®-based material, as described above.

[0016] The combination may further include a thread-carrying bobbin case in the bobbin basket receptacle.

BRIEF DESCRIPTION OF THE DRAWING

[0017] The present invention is described in detail below with reference to the accompanying drawing, in which:

[0018]FIG. 1 is a top plan view of one embodiment of the bobbin basket of this invention adapted for use with a horizontal rotary loop taker in a sewing machine that is equipped with an undertrimmer;

[0019]FIG. 2 is a front elevation view of the embodiment of FIG. 1, as seen from the top of FIG. 1;

[0020]FIG. 3 is a cross-sectional view of the embodiment of FIG. 1 taken along line 3-3 in FIG. 1;

[0021]FIG. 4 is a similar view of the embodiment of FIG. 1 taken along line 4-4 in FIG. 1; and

[0022]FIG. 5 is a similar view of the embodiment of FIG. 1 taken along line 5-5 in FIG. 1.

DETAILED DESCRIPTION OF BEST MODES OF PRODUCT AND PROCESS

[0023] A detailed description of the best modes of practicing the present product and process inventions will now be provided by reference to the accompanying drawings.

General Configuration Of Bobbin Basket

[0024] Plastic bobbin basket 20, seen in top plan view in FIG. 1, includes cylindrical side wall 22 extending around a central axis 23, crosswise support member 24 extending across the bottom of the bobbin basket, center bobbin spool support post 25 extending axially from crosswise support member 24 into a space/receptacle defined by side wall 22, and flange 28 extending radially outward from the top portion of the side wall. Center post 25 carries notch 27 near its upper end to receive a latch for retaining a bobbin case 29 in which the bobbin thread spool is contained. Apertures 25, which are smaller in area than the corresponding apertures of a conventional steel bobbin basket, help to define crosswise support member 24.

[0025] Portions 28 a and 28 b of flange 28 form oppositely facing side walls 30 a and 30 b that are positioned generally radially to form rotation-restraining notch 32 in the top surface of flange 28. First notch side wall 30 a forms the downstream side of rotation-restraining notch 32, relative to the direction of rotation D1 (in FIG. 1, counterclockwise) of the rotary loop taker 31 with which bobbin basket 20 is adapted to be used. Second notch side wall 30 b forms the upstream side, relative to the direction of hook rotation, of rotation-restraining notch 32. Notch 32 is adapted to receive the stud portion of a conventional stationary positioning finger (not shown) with a secure but sufficiently loose fit to permit limited back-and-forth rotational movement of the bobbin basket.

[0026] A second notch 33 is provided at the inside perimeter of flange 28, on the right-hand side of FIG. 1. In use, a projection from the bobbin case that contains the bobbin spool is seated in this notch to align the case properly and to keep the case from rotating on post 25.

[0027] Annular bearing rib 34 extends radially outward from cylindrical sidewall 22.

[0028] The rib 34 extends substantially around the perimeter of the bobbin basket except for a portion of the rib that is omitted at 36 to provide two oppositely facing rib end portions 38 and 40 that define a needle thread pick-up and release area. The rib 34 is guided in the raceway on the rotary loop taker 31 as the rotary loop taker 31 moves relative to the basket 20 around the axis 23.

[0029] Rib end portion 38 forms “T”-shaped pick-up notch 42 at the downstream end, relative to the direction of hook rotation D1, of needle thread pick-up and release area 36 (FIGS. 1 and 2). Rib end portion 40, located adjacent rotation-restraining notch 32, forms a needle thread stop at the upstream end, again relative to the direction of hook rotation, of needle thread pick-up and release area 36 (FIGS. 1 and 2). Needle thread loop 41 comes into contact with stop 40 as the loop is pulled around the bobbin basket and tightened around the bobbin thread (FIG. 2).

[0030] Needle guard plate 46 (shown in FIG. 2) is of the type disclosed and claimed in Applicant's U.S. Pat. No. 4,858,543 referred to above. It is included in the plastic bobbin basket to prevent damage to cylindrical wall 22 if a needle used with the horizontal hook with which this basket is adapted to be employed should be accidentally deflected as it moves toward and into needle-receiving space 48. Plate 46 is omitted from FIG. 1 for clarity.

Damage Resistant Members

[0031] Damage resistant members such as are disclosed and claimed in Applicant's U.S. Pat. No. 5,188,046 are shown in FIG. 1, but are omitted for clarity from FIG. 2. Wear resistant pin 50 protects rib end portion 38, which forms “V”-shaped pick-up notch 42 at the downstream end of the needle thread pick-up and release area. Pin 54 minimizes wear that tends to occur on bearing rib end portion 40 adjacent the upstream end of the pick-up and release area.

[0032] Insert 56 is provided at the upstream side wall 30 b of rotation-restraining notch 32 to minimize impact damage to that wall that would otherwise be caused by the stud portion of the stationary positioning finger referred to above. Pin 60, together with pins 50 and 54, helps prevent wear on the body of bearing rib 34 as the raceway of the associated rotary loop taker 31 slides around the rib at the high rotational speeds at which sewing machines, especially industrial sewing machines, are operated.

Complicated Structure Of Bobbin Basket

[0033] There are hundreds of different types of bobbin baskets employed with industrial sewing machines. Many are used with horizontal hooks, many with vertical hooks and some with zigzag hooks. Each one has a complicated form that is dictated by the functions that are performed by the bobbin basket and by the basket's relationship with the rest of the sewing machine, especially the rotary loop taker (or “hook”) that is used in the machine.

[0034] Some bobbin baskets have even more complicated forms than the basket shown in the accompanying drawing, and others have a somewhat less complicated form. As regards molding problems, however, practically all bobbin baskets have very complicated structures. This is discussed further below.

[0035] As mentioned above, FIGS. 3-5 are cross-sectional views of the bobbin basket of FIG. 1 taken along the respective lines indicated in that Figure. Each of these is shown in an inverted position, to illustrate how the inner and outer portions of a mold, together with various inserts and slides, as required, can be used to produce a plastic bobbin basket by the injection molding process if the polymeric material is in fact moldable. These three Figures also illustrate how complicated the structure of the typical bobbin basket of FIG. 1 is.

[0036] Flange 28, which extends outwardly from the top of cylindrical wall 22 in the lower right-hand corner of FIG. 1, is seen extending from the side wall in the lower left-hand portion of FIG. 3. Bearing rib 34 is shown extending outward from the side wall. Needle thread pickup and release area 36 is not indicated in FIG. 3, but is located on the far side of cylindrical wall 22.

[0037] Rotation-restraining notch 32, with downstream wall 30 a undercut at 62, is seen at the bottom of FIG. 3. Needle-receiving space 48 is located a short distance above notch 32 as seen in this inverted Figure. Aperture 70 is located adjacent the needle-receiving space, and apertures 72 are provided at each end of that space, to receive attaching means for securing metal needle guard plate 46 (seen in FIG. 2) to the plastic bobbin basket.

[0038] Holes are provided for each of the damage resistant members referred to above. Hole 50 a in side wall 22 is adapted to receive wear-resisting insert 50, and hole 54 a is adapted to receive wear-resisting insert 54. A hole is provided in bearing rib 34 and side wall 22 to receive wear resistant member 60 at the location indicated in FIG. 1. (Pin 60 is of course not visible in the cross-sectional views of FIGS. 3-5.) The holes for these three pins just mentioned—50, 54 and 60—preferably extend through both bearing rib 34 and side wall 22. They are preferably insert molded, both for accuracy and to reduce the number of separate mechanical steps required. If the holes are drilled after the basic molding is completed, a diamond or carbide drill must be used.

[0039] The sectional views seen in FIGS. 3-5 are considerably larger than the actual size of the bobbin basket. In the actual life-size basket, the dimensions are very much smaller than they appear in the drawing. In addition to this, a number of thin walls, small ridges, narrow undercuts, small holes and sharp corners are present in the structure of this basket. As will be discussed below, these complexities make for an extremely difficult molding problem at best.

Mechanical Properties of Poly(amide-imide) Resins At High Temperatures

[0040] Plastics that may be considered acceptable for the manufacture of a bobbin basket include high-wear, self-lubricating resins such as ZYTEL 101 (nylon resin) and DELRIN (acetal resin), both marketed by E. I. du Pont de Nemours and Company, ULTM 4001 (polyether amide resin) marketed by General Electric Company and TORLON (poly (amide-imide) resin) marketed by Amoco Performance Products, Inc. Of these plastics, the heat-cured poly(amide-imide) resins have proven to be better than the other available resins in those engineering properties that are critical for any part that is subjected to the extreme conditions under which bobbin baskets are used.

[0041] In use, a bobbin basket is subjected (1) to severe harmonic vibrations caused by the needle thread loops that are pulled forcibly around and along the outer surf ace of the bobbin basket thousands of times a minute (as a result of the high rotational speed of the associated rotary loop taker), and (2) to serious impact forces on the upstream wall of the rotation-restraining notch that are created by the stud portion of the stationary positioning finger when the bobbin basket is jerked back and forth by the needle thread loop as tension is applied to that loop in one direction and then in the other. For these reasons, among others, the plastic of which a bobbin basket is formed must have excellent strength and rigidity.

[0042] The raceway of the rapidly rotating rotary loop taker rubs against the outwardly extending bearing rib of the bobbin basket and tends to create very substantial frictional heat and resulting wear. As the needle thread loop passes around the bobbin basket and is pulled up tight against it, the pressure of the thread as it repeatedly rubs across and along certain portions of the bobbin basket likewise tends to cause frictional heat and resulting wear. It is believed that the frictional heat produced in these two ways may raise the temperature imposed on certain narrowly defined portions of the bobbin basket to several hundred degrees F., or even higher.

[0043] Applicant, years ago, made the surprising discovery that—despite the extremely difficult molding parameters involved—poly(amide-imide) bobbin baskets can in fact be injection molded. Applicant has successfully made and in past years marketed a line of poly(amide-imide) bobbin baskets. To the knowledge of the applicant, while the poly(amide-imide) bobbin baskets have been successfully used worldwide, the performance of these baskets has plateaued in spite of ever ongoing efforts in this industry to still further increase the wear characteristics of these baskets while retaining the desired properties associated with resin bobbin baskets.

[0044] Composite Resin

[0045] The thermoplastic resin in the bobbin basket of this invention is preferably a variation of TORLON® material Grade 4275, previously sold by Amoco Performance Products, Inc. The material which the applicant has incorporated into a preferred form of its bobbin baskets is currently sold by Solway Advanced Polymers LLC commercially as a TORLON® based material under the designation PXM01017.

[0046] Surprisingly, the bobbin baskets made using the TORLON®-based PXM01017 material exhibited very significantly improved wear characteristics compared to bobbin baskets made with conventional TORLON® material of Grade 4275, sold by Amoco Performance Products, Inc. and used by the applicant on a high volume basis over the past several years. Data from comparative testing is provided in the following table and demonstrates the very significant gains made in terms of improved wear. Clearance After 157 h Clearance before test test TORLON ® Material Axial Radial Axial Radial PXM01017 0.05 mm 0.055 mm  0.065 mm 0.10 mm PXM01017 0.05 mm 0.05 mm 0.065 mm 0.11 mm 4275 0.05 mm 0.04 mm 0.066 mm 0.45 mm

[0047] During the testing procedures, the hooks were operated on a stop and go basis for 157 hours, with 2 second stops and 4 second operation at a speed of 4,000 rpm.

[0048] A very significant improvement in radial wear resistance for the guide ribs was observed. The operating forces in a radial direction are generally such as to cause significant radial wear that may necessitate replacement before there is any appreciable axial wear relative to the basket center axis.

[0049] The potential increase in the life of the bobbin baskets attributable to this improved wear resistance is very significant. This increased life not only offers savings in the cost of the baskets, but also by reason of reduced down time and attendant labor costs associated with basket replacement.

[0050] The foregoing disclosure of specific embodiments is intended to be illustrative of the broad concepts comprehended by the invention. 

1. A bobbin basket for use with a lock-stitch sewing machine, the bobbin basket defining a receptacle for a thread-carrying bobbin case, the bobbin basket comprising a wall extending around a central axis and a rib projecting radially from the wall for reception in a raceway of a rotary loop taker to which the bobbin basket can be operably connected, wherein the bobbin basket is molded from a TORLON®-based material commercially sold under the designation PXM
 01017. 2. The bobbin basket for use with a lock-stitch sewing machine according to claim 1 wherein the bobbin basket comprises a center post extending along the central axis in the receptacle for supporting a thread-carrying bobbin case.
 3. The bobbin basket for use with a lock-stitch sewing machine according to claim 1 wherein at least the rib is made from the TORLON®-based material.
 4. The bobbin basket for use with a lock-stitch sewing machine according to claim 1 wherein at least the wall is made from the TORLON®-based material.
 5. The bobbin basket for use with a lock-stitch sewing machine according to claim 1 wherein at least the rib and wall are made from the TORLON®-based material.
 6. In combination: a) a bobbin basket defining a receptacle for a thread-carrying bobbin case and comprising a wall extending around a central axis and a rib projecting radially from the wall; and b) a rotary loop taker comprising a raceway, the rib residing in the raceway and guided within the raceway as relative movement of the bobbin basket and rotary loop taker around the center axis takes place with the bobbin basket and rotary loop taker operably connected, wherein the bobbin basket is molded from a TORLON®-based material commercially sold under the designation PXM
 01017. 7. The combination according to claim 6 wherein the bobbin basket comprises a center post extending along the central axis in the receptacle for supporting a thread-carrying bobbin case.
 8. The combination according to claim 6 wherein at least the rib is made from the TORLON®-based material.
 9. The combination according to claim 6 wherein at least the wall is made from the TORLON®-based material.
 10. The combination according to claim 6 wherein at least the rib and wall are made from the TORLON®-based material.
 11. The combination according to claim 6 further in combination with a thread-carrying bobbin case in the bobbin basket receptacle. 